1. Field of the Invention
This invention relates to a method for surface hardening thermal treatment for steel, to medium carbon alloy steel to be used for the treatment, and to the steel to be produced by the aforementioned surface hardening thermal treatment.
2. Description of the Prior Art
Gears hardened by carburizing have high surface pressure strength and high bending fatigue strength and, therefore, find extensive utility in power lines of automobiles and construction machines. Since the carburizing of gears consumes much time and huge energy, the thermal treatment involved therein is expensive. Since the gears hardened by carburizing undergo heavy deformation during quenching, they are liable to pose problems such as noise and vibration. Not infrequently, therefore, the quenched gears are required to be finished by grinding.
In the circumstance, therefore, development of a method for surface hardening thermal treatment which, unlike the time-consuming treatment of carburizing described above, is capable of quickly producing gears possessing equal or even greater strength than carburized steel and entailing sparing quenching deformation has been in demand.